This invention relates to switched reluctance motors and, more particularly, to a molded end cap-lug assembly which is installed on a rotor assembly of the motor to provide a solid fill of the gap between the rotor poles. The end cap-lug assembly helps eliminate "siren" noise produced during motor operation but does not effect the electromagnetic performance of the motor.
It is known that in switched reluctance motors, there is a certain amount of noise produced by the rotation of the rotor at the motor's typical range of operating speeds. This noise is commonly referred to as a "siren" effect. The source of this noise is due to the countour of the outer surface of the rotor having abrupt changes because the poles of the motor extend outwardly from a central hub of the rotor assembly, with gaps or voids in the space between the poles. This problem has been previously addressed in U.S. Pat. Nos. 5,053,666 to Kliman et al., 5,023,502 to Johnson, and 4,916,346 to Kliman. In each of these earlier attempts at solving the noise problem, the gaps or interpolar spaces between the rotor poles are filled with a material which can be an electrically insulating material. The respective forms of construction utilize segments such as stacked laminations which are inserted in these spaces and then welded in place as taught by Kliman and Kliman et al.,; or, a molded insulation material is inserted in the gap as taught by Johnson. To further help hold the rotor laminations in place, the design of the rotor laminations are modified so that, as shown in the Johnson patent, tangs are formed on the inner curved surface of the lamination at the inner end of the respective gaps, the tangs having a keystone shape. The molded insulation has a corresponding slot so to be fitted into the interpolar space. Kliman et al. (see FIG. 3) employs indentations along the sidewalls of the rotor teeth with the inserts having corresponding bumps so to maintain the laminations of insulating material locked in place. Rotor designs for switched reluctance motors have two basic constructions. In one construction, the poles of the rotor are defined by straight side walls which extend outwardly from a central rotor hub. These are the type rotors where the tangs are indentations help retain the inserts in place when the motor is operating at speed. The other rotor design has shoulders formed at the outer end of the pole and extending circumferentially into the outer portion of the the gap so to overhang the gap and provide an outer shoulder to lock an insert in place.
While the above patents indicate a recognition of the noise problem, the solutions taught by these patents are not necessarily the most cost effective. Adding tangs or indentations to a rotor lamination increases the cost of the lamination and effects the electromagnetic characteristics of the rotor. Welding laminations in place, or gluing them will not necessarily prevent inserts from breaking loose over time and damaging or ruining a motor. The extra steps involved, as part of the rotor fabrication process, to mount and affix the laminations or inserts in place add cost to the motor. Replacement of the inserts or molding requires replacement of the entire rotor assembly because of the way the inserts are attached to the rotor. The size and weight of the inserts or molded parts add substantial weight to the rotor assembly because of the volume of material they contain. It will be noted that, in general, the laminations and molded pieces are solid pieces of whatever material from which they are made. In sum, there is a more cost effective solution to the noise reduction problem which avoids certain of the drawbacks found in the previous attempts to solve the problem.